Master & Slave
As the era progressed, the thirst for knowledge and research increased. Scientists and researchers were in constant need of human specimens for research and experiment purposes...
One of the many wonders of science made it possible to delay death. This usually involved replacing defective organs of an individual; either through cloning or with compatible organs of another person. The former has minor side effects while the latter almost none.
This meant a heavy demand for organs...
If history has thought something, it was that whenever there has been even a slightest need or demand for something, shrewd minds would turn it into a successful business model.
Prostitution, health, education, food, water...
The same applied to demand and need for organs and specimens. Human trafficking and organ harvesting have bloomed into an illegal but wonderful business.